The present invention relates to the field of machines that allow a machining by the removal of material by reproducing a model, more particularly applied to the medical field, particularly the dental field, for manufacturing ceramic components intended to replace all or part of a dental crown, and relating in particular to machines comprising a machining tool with an axis of symmetry and having at least one degree of freedom in rotation about said axis of symmetry, means for driving the rotation of the said machining tool about its axis of symmetry, means of securing a blank, in which said volume is machined, having at least one degree of freedom in rotation, means for driving the rotation of said blank-securing means, means for securing a template, having at least one degree of freedom in rotation, means for driving the rotation of said template-securing means, a feeler capable of coming into contact with the exterior surface of said template, means for bringing about relative movement between said blank-securing means and said machining tool, on the one hand, and between said template-securing means and said feeler on the other hand, said movement means allowing the machining tool and the feeler to remain in constant contact with, respectively, said blank and said template.
A known method and to an apparatus for manufacturing volumes by copying in. dentistry, particularly for inlays, is disclosed in U.S. Pat. No. 5,135,393. The machine is an eight-axis machine in which all movements of the moving parts of the machine are performed manually by the operator, except for the rotating of the tool which is done by a motor. More specifically, the machine comprises a first carriage carrying a feeler and a tool support which are held together, the axes of which are mutually parallel and are perpendicular to an axis of movement and translation of the feeler and of the tool support; furthermore, this first carriage is free to rotate and to translate along axes respectively parallel and perpendicular to the axis of translation of the feeler and of the tool joined together; this first carriage is kept pressing and moved by an operator during machining against a second free-rotation carriage which carries the template and the blank themselves which are free to rotate on this second carriage; so that under the pressure and movements brought-about by the operator, the feeler travels over the surface of the template and the tool machines the blank accordingly; the template and the blank are incidentally linked in rotation so that when the operator with one hand turns the template, the blank follows this rotational movement, whereas with the other hand the operator takes care to cause the feeler to travel over the surface of the template. A machine such as this is complicated and expensive because of the high number of degrees of freedom and is tricky to use because the copying precision depends on the quality of service provided by the operator.
The prior art in particular teaches a machine of this type with document WO 96/05 782, comprising a diamond-tipped machine tool actuated by a high-speed turbine, a feeler placed on the same machine body of the tool, the tool and the feeler being able to move in translation and in rotation so as to follow the profile of a model secured in alignment with the blank, such a machine allowing a model to be reproduced precisely but entailing a mechanism which is cumbersome, bulky and expensive, particularly because of the high speeds at which the tool rotates. Furthermore, the small-diameter tool which allows small details to be reproduced, which rotates at high speed, may wear rapidly and therefore cause the machine to be expensive to use.
The present invention essentially sets out to alleviate these drawbacks and to provide other advantages. More specifically, it consists in a machine for machining at least one volume, particularly an inlay, automatically by copying, comprising at least:
a machining tool with an axis of symmetry and having at least one degree of freedom in rotation about said axis of symmetry,
means for driving the rotation of the said machining tool about its axis of symmetry,
means for securing a blank, in which said volume is machined, having at least one degree of freedom in rotation,
means for driving the rotation of said blank-securing means,
means for securing a template, having at least one degree of freedom in rotation,
means for driving the rotation of said template-securing means,
a feeler capable of coming into contact with the exterior surface of said template,
means for bringing about relative movement between said blank-securing means and said machining tool, on the one hand, and between said template-securing means and said feeler on the other hand, said movement means allowing the machining tool and the feeler to remain in constant contact with, respectively, said blank and said template,
means for commanding and controlling said means for driving the rotation of the machining tool, said means for driving rotation of the template-securing means and said movement means, said machine being characterized in that said machining tool is an abrasive disk and in that said movement means comprise a moving carriage on which said blank-securing means and said template-securing means are mounted so that they are free to rotate, said moving carriage having at least two degrees of freedom of movement.
The abrasive disk which makes it possible to reduce the rotational speed of the machining tool appreciably, and the arrangement of the movement means which allow the blank and the template to be moved rather than the machining tool, lead to a significant reduction in the weight and cost of the machine.
According to an advantageous characteristic, said two degrees of freedom of said moving carriage are one degree of freedom in rotation and one degree of freedom in translation, and said movement means comprise means for driving the translation and means for driving the rotation of said moving carriage.
According to an advantageous characteristic of the foregoing, the machine according to the invention comprises a rigid support, and said means for driving the translation of said moving carriage comprise a first motor connected completely to said rigid support, in that said means for driving the rotation of said blank-securing means and said means for securing the template comprise a second motor connected to said first motor via a screw-nut connection, and said moving carriage is free in rotation about the output shaft of said second motor, said output shaft being guided in rotation and in translation by said rigid support.
According to an advantageous characteristic of the foregoing, said means for driving the rotation of said moving carriage about the output shaft of said second motor comprise the friction forces generated by the rotation of said blank-securing means and of said means of securing the template.
According to an advantageous characteristic of the foregoing, said blank-securing means and said means for securing the template are connected completely and have aligned axes of rotation.
According to an advantageous characteristic of the foregoing, the axis of rotation of said abrasive disk is parallel to the axes of rotation of said blank-securing means and of said means for securing the template, said rigid support having a flat wall perpendicular to said axis of rotation of the abrasive disk separating a machining compartment from a drive compartment.
According to an advantageous characteristic of the foregoing, the axis of rotation of said abrasive disk and the output shaft of said second motor are mounted in identical respective bearing supports.
The flat wall perpendicular to the axes of rotation makes the bearing supports easier to mount and the use of identical bearing supports lowers manufacturing costs.
According to an advantageous characteristic, said feeler is secured rigidly to said rigid support so as, by its abrasion resulting from the rubbing against the template, to compensate for the wear of said abrasive disk, thus making the precision of the reproduction independent of tool wear.
According to another advantageous characteristic, the machine according to the invention comprises means of moving said feeler radially, making it possible to establish a given dimensional ratio at which the inlay is reproduced with respect to the template, in a plane perpendicular to an axis of rotation of said template.
This characteristic allows the radial reproduction ratio to be varied without varying the axial reproduction ratio, used particularly the case of the manufacture of inlays, so as to form a cementing space or so as to compensate for errors which may impair the fit, without this detracting from the longitudinal dimension.
According to another advantageous characteristic, said feeler has a thickness greater than the thickness of said abrasive disk so as to increase the longitudinal dimension of the inlay with respect to that of said template.
Aside from compensating for errors in flatness or due to the vibrations of the disk, this characteristic allows compensation for the removal of material carried out when the finished part is polished.
According to another advantageous characteristic, said blank-securing means and said means for securing the template are connected by a screw-nut connection, said blank-securing means being secured rigidly to one of said elementsxe2x80x94screw or nutxe2x80x94and said template-securing means being secured rigidly to the complementary other one of said elementsxe2x80x94nut or screw.
This characteristic allows a more ergonomic machine according to the invention, the blank-securing means being fastened to the template-securing means by a screw-nut connection. Thus, the operator can easily, with two hands, assemble the blank and the template, each held in a respective hand, and, through the reverse movement, disassemble the part obtained from the template, and do so without immobilizing the axis of rotation thereof. This characteristic also makes it possible to eliminate any play there might be between the blank and the template.
According to another advantageous characteristic, the machine according to the invention comprises means for automatically stopping operation at the end of machining by detecting that said moving carriage is in a given position. At the end of machining, as the feeler no longer holds the template, the moving carriage moves toward the axis of symmetry of the abrasive disk, it being possible for the automatic stop means to be advantageously actuated during this movement.
According to another advantageous characteristic, the machine according to the invention comprises a disk which is abrasive over all or part of its two opposite faces, said two opposite faces converging toward the periphery of the disk. As the disk essentially works on a face in opposition to the movement of the moving carriage, turning over the disk, one face of which is worn, makes it possible to double the life of this disk.
According to another advantageous characteristic, the machine according to the invention comprises means for slaving said movement means to the force exerted by the abrasive disk on the blank. A characteristic such as this makes it possible to optimize the machining time.
According to another advantageous characteristic, the machine according to the invention comprises means of lubricating said machining disk by splash lubrication. This characteristic makes it possible to avoid the use of a machining lubrication circulation pump.
According to another advantageous characteristic, the machine according to the invention comprises means for reversing the direction of rotation of said abrasive disk. It is therefore possible to use the two opposite sides of the abrasive grains of a disk, thus optimizing the cost of using the machine.
According to another advantageous characteristic, the machine according to the invention comprises means for automatically clearing said moving carriage at the end of machining. This makes it possible to achieve better ergonomics, automatically clearing the carriage at the end of machining allowing easier access for disassembling the machined part and the template.
According to another advantageous characteristic, the machine according to the invention comprises a centering jig allowing the blank to be secured to said blank-securing means, and allowing the template to be secured to said template-securing means in such a way that the inlay to be obtained lies within the volume of the blank. This characteristic makes it possible to avoid the volume which is to be machined being positioned with respect to the template in such a way that the volume would lack material with respect to this template.
According to another advantageous characteristic, said blank and said template are secured to their respective securing means via at least one of their respective ends.